French patent application FR 2 754 579 filed in the name of the Applicant company on Oct. 15, 1996 and published on Apr. 17, 1998 describes a damper of that type in which the damper assembly comprises firstly a hydraulic damper device disposed in a viscous fluid cavity, and secondly a flexible device presenting high stiffness in a direction parallel to said main axis and low stiffness in the direction perpendicular to the main axis. That hydraulic damper device is constituted by first and second sets of plane vanes each having its plane extending perpendicularly to the main axis, the first set being secured to the driving element and the second set being secured to the rigid element, the vanes of the first and second sets being disposed in interleaved manner and being spaced close together so as to present viscous damping zones each situated between a vane of the first set and a vane of the second set.
The damper device having interleaved plane vanes as described in the above-specified application enables good performance and good linearity to be obtained for vibration at low or medium amplitude. However, as the amplitude of vibration increases, the relative speed between the vanes also tends to increase, thereby increasing shear and decreasing dynamic viscosity, and as a result the damping provided by the hydraulic device tends to diminish.
Viscous damper devices are also known that enable high damping to be obtained with large amplitudes of displacement since the damping provided is proportional to the square of speed, but they suffer from poor efficiency at low amplitudes.